"This has never been seen before in a cephalopod, and in an animal with external fertilisation," says Wegener, who carried out the research as part of his PhD.

The ejaculate of most species contains nutrients to help the sperm survive, and such nutrition can provide a nourishing food source -- especially for the energy-sapping process of sex.

"Everything about sex is costly. The act of mating itself is risky. You can get diseases, you can get eaten by a predator and it distracts you from foraging for food," says Wegener.

"If an individual can exploit another's reproductive investments they can get a pay off from the act of sex."

Unexpected finding

When Wegener and colleagues started observing the sexual behaviour of southern bottletail squid (Sepiadarium austrinum) from Melbourne's Port Phillip Bay they never expected to see what they did.

Once together in the observation tank the male and female squid got straight to business.

"They just mated straight away and you could actually see the female eat the spermatophores [packets of sperm]," says Wegener.

The researchers would never have seen this if the animals were not almost transparent, making it easy to tell which sex they were, and to observe the females eating the spermatophores.

The male shoots his spermatophores at the female and they stick to an open pouch around her beak, called a buccal cavity.

Some of the spermatophores land at the base of the female's beak, on what Wegener refers to as "prime real estate". It's prime because they are in a good position for egg fertilisation. Females then use their tentacles to run the eggs over the spermatophores cemented to her front.

"Any sperm that she uses for egg fertilisation comes from there," says Wegener, adding that the female has three weeks to fertilise her eggs because the sperm will degrade after this time.

But some of the sperm packets get stuck a bit further out on the female's buccal cavity where she can reach them with her beak.

"She uses her beak to scrape them off and eat them," says Wegener.

He says the findings are consistent with the idea of the female consuming the ejaculate to help fuel her sexual activity, but further research needs to be done to confirm whether this is the case.

"We need to find out if eating the ejaculate gives her offspring an advantage," says Wegener.

He says such a phenomenon is rarely seen in nature, although a few animals including leeches and flies are known to consume sperm.

In flies, says Wegener, harassed females give in to copulation but afterwards expel the ejaculate including sperm and consume it.